PROJECT SUMMARY Although small-molecule intracellular metal catalysts (SIMCats) offer potentially powerful new ways to manipulate biological systems, several scientific barriers to their development have unfortunately limited their use in life science research. The long-term goal of this project is to establish a comprehensive SIMCat discovery program that focuses on their development and translation from the reaction flask to living systems. The overall objectives of this research are to 1) identify the factors that are important to obtaining fast, selective, and biocompatible transfer hydrogenation SIMCats; and 2) create new catalytic agents for the remediation of aldehyde overload. We are interested in SIMCats that catalyze transfer hydrogenation reactions because they mimic important redox enzymes that are ubiquitous in all life forms. Our central hypothesis is that these synthetic enzyme mimics could be used to neutralize toxic aldehydes in vivo so that endogenous antioxidants, such as glutathione, are free to sequester reactive oxygen species that damage cells and tissue. The rationale for this project is that by selectively converting toxic aldehydes to non-toxic alcohols, transfer hydrogenation SIMCats could supplement Nature?s defense system against oxidative stress. SIMCats are expected to be highly efficient detoxification agents due to their ability to catalyze continuous reaction turnovers, unlike conventional aldehyde scavengers that get consumed upon each reaction. In Specific Aim 1, a variety of half-sandwich metal complexes will be tested for their activity and the most promising candidates will be subjected to structure-activity relationship and kinetic/thermodynamic studies to obtain chemical insights into their catalytic behavior. In Specific Aim 2, the catalytic rates, speciation, and distribution of SIMCats inside live cells will be determined. This aim will be accomplished by taking advantage of single-molecule super resolution microscopy and ratiometric fluorescence imaging techniques to visualize SIMCats ?in action.? In Specific Aim 3, the ability of transfer hydrogenation SIMCats to protect neuroblastoma cells and zebrafish against aldehyde toxicity will be evaluated. The efficacy and aldehyde selectivity of SIMCat detoxification agents will be compared to that of conventional stoichiometric aldehyde traps. The significance of our research is the development of synthetic methodologies that are tailored toward the discovery of novel SIMCats, which considers not only chemical reactivity and substrate selectivity but also biocompatibility. The innovation of our research is the application of organometallic complexes to protect cells against chemical toxicants by exploiting their catalytic capabilities. We expect that this work will help streamline the SIMCat discovery process and lead to new approaches to remedy aldehyde overload, which could have important therapeutic relevance to the treatment of oxidative stress-related diseases in humans.